After another (too) long hiatus, I finally took a peek at the Drawpile codebase again. Managed to fix the alpha blending problem that had stymied me last time to such extent that it had put me off coding DP for all this time. Today I felt an inspiration to take another look and I fixed the problem in five minutes. Just goes to show that sometimes you need to take a break and get a fresh perspective.
Also, DP's source code is now hosted at GitHub. For a long time I've been wanting to switch over to Git from SVN and now seemed like a good time. The ability to create local branches was something I really wished for back when I was writing the first version of DP's tile based core.
OpenRaster has seen some development since the last time I looked at it, so DP's ORA support has to be updated to match the latest spec. Maybe use libora?